This finding is surprising because no serious clinician has any idea how this could possibly work. Most miscarriages are caused by chromosomal abnormalities. Caffeine does many things, but nobody has ever shown that it harms chromosomes. It’s difficult to imagine how caffeine could possibly cause miscarriage. Is this harm real?

Anytime the press reports a possible peril to a developing fetus, it’s easy for the report to add an item to the list of pleasures that are prohibited during pregnancy. Here’s how:

Pretend that we’re concerned that watching television might harm a fetus. (It sounds plausible, right? As a society we believe that some things are likely to cause harm that we do not yet know, and these things include caffeine and television.) Let’s do a thought experiment that could make a medical researcher famous.

1) Give questionnaires to some women. Ask how much TV they watched during pregnancy. 2) Ask about lots of bad things that could possibly happen to a developing child: Obesity, prematurity, attention-deficit-hyperactivity disorder, and more.3) Send the questionnaires to statisticians; instruct them to analyze the results in hundreds of ways.

If you analyze imperfect data in enough ways, you can always find some meaningless, coincidental correlation. Biostatisticians call this practice “data dredging.” This technique frequently yields misleading results, but some researchers do it anyway. This is how the caffeine/pregnancy study was done. Our health journalists could have ignored this exercise in data dredging, but, instead, they broadcasted it on TV.

Back to the thought experiment. Imagine that the statisticians dredge up a correlation between watching television in pregnancy and having a child with Down syndrome.

4) Publish the result.

Down syndrome, just like miscarriage, is caused by a chromosomal problem. It’s completely unknown how television—or caffeine—could possibly harm chromosomes. However, now the American Pregnancy Association states that women should minimize caffeine intake, even though they acknowledge that studies on this topic have been “inconclusive.” How do they explain their recommendation? “It is still better to play it safe when it comes to inconclusive studies.”

Our television study was also inconclusive. I suppose it’s always better to “play it safe,” after every study result, no matter how flimsy. No more coffee (miscarriage) or TV (Down syndrome) for pregnant mothers!

Yes, this thought experiment is inane. However, it’s difficult to show how it is different from the caffeine study. There are other, worse flaws with the methods of the caffeine study, making it difficult to conclude anything from it. Good science may someday show that tiny amounts of caffeine in pregnancy cause harm. However, seeing how little we know, it may turn out that caffeine is actually beneficial in pregnancy. We just don’t know. This study didn’t tell us any more about caffeine than our thought experiment told us about television.

This is not trivial. Thousands of women will suffer headaches from caffeine withdrawal as a result of this study. In exchange for their headaches, these women receive protection from a condition that caffeine probably cannot cause.

Let them drink coffee.

*The proper study design to answer this question is a randomized, placebo-controlled, double blind clinical trial. This sort of data dredging study—the one reported in the Times—is, as described above, largely useless for answering a clinical question.

This blog is not intended to diagnose, treat, cure or prevent any condition or disease. Please consult with your own physician or health care specialist regarding the suggestions and recommendations made within.

Excellent post. Two points I might add:
1. You note that not knowing how caffeine might cause harm doesn't stop scientists from concluding that it may. This is the same non-rational "science" that underlies many medications. Aspirin, Prozac, angioplasty, and many other meds and procedures have been routinely employed without any serious understanding of how they work.
2. This seems one area where an evolutionary perspective may be useful. It stands to reason that many of the substances/experiences encountered in the ancestral environment would be unthreatening to us, as we've had the opportunity to evolve defenses. In fact, many of the seemingly threatening substances have been shown to be beneficial (e.g., diseases caused by the lack of exposure to soil-borne pathogens). I suspect TV and caffeine are potent threats (real or not) because they did not exist until recently and so people instinctively suspect they may be vulnerable to them on some cellular level.

I am 3 and a half months pregnant with my first child...I don't over eat, I take my pre-natal vitamin...but have been beating myself up about my caffeine intake....I am a healthy weight for my height with a 21.4 BMI and I am 31....Caffeine has been my drug of choice for years. I never smoked, never did drugs, never was over weight and was always active. In fact I never was a big pill popper either. I had to be really sick to take over the counter medication. Not so much coffee but pop....Pepsi, I love and I just don't feel good if I don't have any....after about 3 days with a reduced intake I start going through withdrawls.

I finally told myself that pop has been around for years and women have been having babies (healthy ones)since the begining of time before all of these rules came out.

Being an expectant mother is hard enough without having to give up EVERYTHING that you love.

Enjoyed reading this. Every week there is a new click bait headline leading to an article that puts a great amount of unnecessary fear in pregnant women. Somebody, somewhere, must be making decent money off of these studies that are usually inconclusive and rarely involve more than a couple of hundred mothers-to-be. It doesn't end after you've given birth either! No wonder there are "mommy wars." All of these anxious women brainwashed by studies, worrying if they are bad mothers, going around judging other moms just to make themselves feel better about that Coca Cola they had while pregnant that probably didn't *BUT MAYBE IT DID* cause their son's ADHD. Sad...

I am very similar to the commenter above. I don't take over the counter meds, alcohol, and I eat organic vegan and stay in good shape by walking, although I could exercise more. My guilty pleasure is big iced coffees (black unsweetened) and iced teas. I'll get an extra large iced green tea and sip on it all day long, and I don't like plain water, never have. Most of the time my caffeine intake stays at 100-200mg daily because I do decaf and herbal or green, but once in awhile it clocks closer to 300 if I had any soda or black tea, or 2 big green teas. I've had my fingers crossed this is still considered "in moderation." It seems pretty conservative. Recently I learned a fetus doesn't have the ability to process caffeine like we do, it lacks the enzyme or some such thing. If that's true then his could any amount be safe or 0 impact. It's got me worried but I have not seen anything conclusive. I also just read a govt study that showed "statistical significance" between caffeine and certain birth defects, yet concluded the jury is still out on that too. If the fetus can't process caffeine it seems a wise thing to abstain from. Bummer!

Good to hear from you.
It's too bad that we don't have clinical trial data to help guide you with your decision about how much caffeine to drink--it's entirely possible that caffeine consumption in the amounts you describe could be beneficial to your fetus, or harmful, or neither. We just don't know, which leaves you in a frustrating position when you try to make decisions about what to do today. We go into life with the scientific knowledge we have, not the knowledge we wish we could have.

Dr. Siegel, your analysis is certainly not comprehensive on this subject, and when there are studies out there that do significantly indicate a correlation between caffeine and harm to the fetus, why wouldn't you err on the side of caution? It could be sound wisdom considering that a woman only has one chance at growing their baby inside her. Dr.'s like yourself created articles like this one decades ago when they were trying to comfort women by telling them that they didn't have to give up smoking while pregnant.

So many times women have miscarriages and no one ever knows what caused it. At the same time their are more and more studies showing possibly negative impact to babies in the womb, especially during the first trimester. Again, there is ever increasing proof of the link between caffeine and fetal related issues. You wrote this article 8 years ago, but so much has come out since then concerning this issue. Let me put it to you this way. NO ONE knows exactly how much caffeine intake is SAFE for a pregnant mom. Every woman's body is different, every child's body is different, every cord is different, every placenta is different. There are other factors involved as well like whether caffeine sensitivity runs in the family, etc.

You say how people often read articles about things that could be harmful and they get scared and decide to cut out a bunch of stuff, but isn't it far worse for the opposite to happen. Many times people look for articles that say that it is ok to continue their addictions so that they can justify them. Like I mentioned earlier, decades ago women smokers felt great relief when they read an article like this one from a doctor telling them that there is not enough evidence about smoking while pregnant, and that they should not worry about it and just continue on smoking.

Which side would you rather be on, the side that uses wise caution or the one who just tells people what they want to hear concerning continuing their habits/cravings/addictions. Which side of the smoking debate would you have been on decades ago?

Let me tell you my story. An irregular heartbeat was found in my son Isaac while he was in the womb. It just happened to be noticed at a regular wellness exam (often heart rhythm issues, etc are not caught at these brief exams, but thank God this was). We took him to the heart specialist and my son had an extra beat in the upper chamber once every 3-5 beats. The lower chamber could not keep up. The specialists called it a PAC. The specialist could not see anything wrong with the heart, and then finally asked my wife about caffeine intake. She was asked about whether she used stretch mark creams, ate chocolate, etc. Then we told the specialist that my wife drinks a venti chai tea latte with an extra pump every day. The specialist told her to stop the caffeine, and that if the caffeine was the root cause then the PAC will slow to once every 10-15 beats in about a week. We went back one week later and the PAC had slowed to once every 12 beats...........precisely indicating that the caffeine was the root cause. Within another week, the PAC was completely gone. So, of course, my wife stayed off caffeine for the rest of the pregnancy.

Let's use some reasoning here. Adults go to the hospital all the time for irregular heart beat issues and other issues related to stimulants such as caffeine. My dad has gone multiple times for a racing heart beat and was told to back off caffeine. If it can effect adults that way then think about how much more so a tiny, developing, vulnerable baby in the womb. Again, a woman only gets one chance! Babies in the womb (especially during the crucial 1st trimester) cannot process and eliminate caffeine from their body nearly as effectively as the mom can. So, while momma is ready for today's dose of caffeine, many times the baby in the womb hasn't yet finished processing yesterday's portion. It can build over time to unsafe levels. That is another reason why NO ONE can say how much daily caffeine intake is SAFE, except of course to avoid it completely while pregnant for your baby's sake! Most moms however don't really realize how much caffeine they are actually in-taking anyway. I didn't know how much was in various drinks until I looked it up, but how many actually do that? Do pregnant women really keep up with how much caffeine they intake from creams, chocolate, sodas, coffee, etc? I would venture to say that most do not. And when they read articles like this, they don't think that they need to.

Did the doctors who told moms decades ago that smoking was ok during pregnancy ever come back and apologize to those moms who's babies were impacted as a direct result of smoking? Will you ever go back and apologize about your dismissive analysis concerning caffeine during pregnancy?

The evidence for caffeine correlating in some way to first trimester miscarriage and other fetal harm is already out there, but how many moms will just read your article and think that they don't need to know anything else? You've told them what their itching ears want to hear. Ignorance is bliss, right?

Hopefully you will update your research and err more on the side of wisdom when advising pregnant moms.

Here are just a handful of articles implying that significant caution should be taken by moms concerning the risks of caffeine during pregnancy: